The Wall Street Journal reports that the Yahoo CEO was scheduled to meet a group of ad executives for a private dinner during the Cannes Lions festival in France last Tuesday, but showed up "nearly two hours late" because she had fallen asleep.

One executive in attendance from IPG is said to have left before Mayer arrived.

A rep declined to comment on whether Mayer overslept the appointment, but told Mashable in a statement that "we value our partnership with IPG and all of our advertisers".

The incident may have simply been the result of jet lag, but it seems to have reinforced the narrative that Mayer and Yahoo are having difficulty wooing advertisers.

"It is another instance where she demonstrated that she doesn't understand the value of clients, ad revenue or agencies," one anonymous ad executive at the dinner told the Journal.

After a different appearance from Mayer at Cannes, some criticised her for being too scripted and making a presentation that felt too much like "a sales pitch".

Mayer took over as CEO of Yahoo nearly two years ago. Since then, she has worked to improve Yahoo's mobile presence through a number of acquisitions and double down on its media efforts. Yahoo's stock has soared in that time, but many credit that to Yahoo's stake in Alibaba, which is about to go public.

Yahoo's display ad revenue ticked up by a modest 2 per cent last quarter compared to the same period a year earlier, though its price per ad declined.